This invention relates to an engine control system and more particularly an improved sensor arrangement for such a system as particularly applied to two-cycle crankcase compression internal combustion engines.
The advantages to two-cycle internal combustion engines because of their simplicity and relatively low cost are well noted. However, the porting arrangement for these engines gives rise to certain problems in connection with exhaust emission control. Because of the overlap between the scavenging action and the exhaust, there is some difficulty in insuring good exhaust emission control. This is because some of the scavenging charge may actually pass out the exhaust port, and thus present the risk of unburned hydrocarbons escaping to the atmosphere.
In addition to this problem, because of the fact that the lubricant in a two-cycle engine is normally not recirculated but is consumed in the engine during its running, there is a likelihood of lubricant in the exhaust gases. Thus, this type of engine presents particular problems in controlling exhaust gas emissions.
Such features as the use of fuel injection and exhaust gas treatment as well as feedback controls have been proposed so as to permit the continued use of two-cycle engines, even in spite of environmental concerns. However, the use of some of these exhaust control methods also are made difficult by the inherent nature of the two-cycle engine operation.
For example, it has been the practice in four-cycle engines to use feedback control systems to maintain the desired air/fuel ratio under all running conditions. These feedback control systems employ oxygen sensors in the exhaust or other sensors to insure that the air/fuel ratio is maintained within the desired range and also to control exhaust emissions. The most commonly used type of sensor senses the presence of oxygen in the exhaust gases in order to provide an indication as to whether or not a stoichiometric mixture is being burned. However, due to the scavenging effect and the likelihood of some air charge in the exhaust gases, oxygen sensors may not be completely practical in these applications. This is because the oxygen sensor may receive some oxygen rather than exhaust gases during the final portions of the exhaust scavenged phase. Devices have been proposed for attempting to overcome these problems, but for a variety of reasons they have not been particularly successful.
It is, therefore, a principal object of this invention to provide an improved engine management system particularly adapted for use with two-cycle crankcase compression engines.
It is a further object of this invention to provide an improved sensor arrangement for feedback control in such engine management systems.
It is a still further object of this invention to provide an improved exhaust sensor arrangement for a two-cycle crankcase compression engine wherein the sensor is mounted and operated in such a way as to insure that primarily exhaust products will be delivered to the sensor.
In order to permit more accurate exhaust gas sensing in two-cycle engines, it has been proposed to provide an oxygen sensor arrangement wherein the oxygen sensor receives gases directly from the combustion chamber but only at times when the scavenging process is not at such a stage where the scavenge gases may contact the oxygen sensor. However, the type of systems proposed for this purpose have, for the most part, required some form of valving arrangement for insuring that the oxygen sensor only receives exhaust gases. This provides not only a complicated structure, but also a possible source for malfunction.
It is, therefore, a still further object of this invention to provide an improved oxygen sensor arrangement for two-cycle engines wherein it can be insured that the sensor receives exhaust products from the engine but not scavenging gas products.
As has been previously noted, the exhaust gases in two-cycle engines may contain amounts of lubricant. The type of exhaust sensors utilized for engine management systems are relatively sensitive and can be easily contaminated if lubricant comes in contact with them.
It is, therefore, a still further object of this invention to provide an improved exhaust sensor arrangement for an engine wherein the sensor, per se, is protected from contamination.
The type of exhaust sensors used for engine management systems are also sensitive to vibrations and mechanical shock and can be disabled if subjected to an impact force. It is, therefore, a still further object of this invention to provide an exhaust sensor arrangement for an engine wherein the sensor is protected from potentially damaging mechanical shock.